The present invention relates to a track-bound vehicle converter as well as a track-bound vehicle having at least one such converter.
Such a converter is arranged in a track-bound vehicle, such as a rail vehicle, for converting a direct voltage to an alternating voltage or vice versa for different purposes. The invention also includes indirect AC/AC converters, i.e. converters with two stages, interconnected on their DC sides. The invention is not restricted to any number of phases of this alternating voltage, although single phase and three phase voltages are most common, neither is the invention restricted to any particular levels of such voltages or electric power to be fed through said converter.
The present invention is primarily directed to an auxiliary converter, i.e. a converter configured to deliver a voltage on the converter output to be used for electrical appliances, such as through socket outlets arranged in the track-bound vehicle and the heating/cooling system of the vehicle. However, the invention does also cover motor converters configured to deliver power through the converter output to a motor used to drive the vehicle as well as line converters configured to                in driving mode absorb power from the AC supply line via the main transformer connected to its AC side and feed it to the motor converter connected to its DC side and        in braking mode absorb power from the motor converter and feed it to the main transformer and back to the AC supply line.        
FIG. 1 illustrates schematically how these three types of converters may be arranged in a track-bound vehicle 1. It is shown how the vehicle is in this case configured to move along an AC-supply line 2, which accordingly acts as a AC-source and which may for example carry an one-phase alternating voltage of 15 kV and 16⅔ Hz (Sweden) and 25 kV and 50 Hz (Denmark). The vehicle has a transformer 3 for transforming the voltage from the supply line 2 to a suitable level. The transformer has here two secondary windings 4, 5, one of which being connected to a converter 6 for delivering a direct voltage of for example 1.5-3 kV on the output thereof. This direct voltage is delivered to an auxiliary converter 7, which is controlled by a control unit 8 for generating a train of pulses according to a Pulse Width Modulation pattern for delivering a three-phase alternating voltage on the output thereof. The output of the converter is connected to a three-phase transformer 9 as well as harmonic filters 10 for smoothing out the alternating voltage delivered by a distribution network 11 to sockets arranged in the track-bound vehicle, such as for connection of computers, and to lighting, heating and other appliances.
The other secondary winding 4 of the transformer 3 is connected to a converter 12 configured to deliver a direct voltage on the output thereof to the input of a motor converter 13 controlled by a control unit 14 in a similar manner as the control carried out by the control unit 8 for delivering a three-phase alternating voltage on the output thereof to motors 15 in the form of electric machines, for driving the vehicle. The control unit 14 will receive orders from the driver of the vehicle for adapting the frequency of the voltage delivered to the stator windings of the motors to the vehicle speed being desired. In the case of braking the vehicle electric power will flow in the direction from the motors to the AC-supply line 2 through the converter 12 then acting as a line converter controlled through a control unit 16 to deliver a single phase alternating voltage on the output thereof.
The invention is just as well directed to track-bound vehicle converters to be used in vehicles fed by a power supply line in the form of a DC-source, and in such a case the part to the left of the dashed line 17 in FIG. 1 is not needed, but the direct voltage supply line will then be connected via a line filter inductor to the direct voltage side of the converters 7 and 13 close to said dashed line 17. However, the DC-power supply line may then be connected to a DC/DC-converter controlled by a control unit if the DC-power supply voltage is for example 3 kV for adjusting the supply voltage level to the motor converter 13 and the auxiliary converter 7 to for example 1 500 V.
The control units 8, 14, 16 of these converters utilising a Pulse Width Modulation (PWM) scheme for controlling the converters which produces voltage pulses on the outputs thereof with steep flanks, such as in the order of 2 000 V/μs, resulting in high requirements of insulations, such as in bearings, stator winding pockets and so on for avoiding creation of detrimental eddy currents. Furthermore, heavy and costly filters (only shown for the auxiliary converter in FIG. 1) have to be connected to the outputs of these converters for removing low and high frequency harmonics resulting from the switching of components of the converters producing the pulses.